We developed a robust method for estimating lip position that is independent of camera zoom and direction of the face. The method require no extra information about position or form in advance. The method was carriedout without limited conditions such as lipstick or lighting because lip is generally redder than the skin. The method makes use of the psychometric quantities of rectangular coordinates (a*) and color difference (Δa*), which are defined in theCIE 1976 L*a*b* color space. The CIE 1976 L*a*b* color space separates chroma channels and lightness, and it is nearly perceptually uniform. The method extracted the outer-lip contour based on the Δa* values. Furthermore, we estimated the lip position with the aid of the a* color histogram. The results indicated the effectiveness of this method; the image data was used to estimate the lip's position with about 96-percents accuracy.
